Heretofore it has been well known to utilize optical systems on aircraft for purposes of taking continuous aerial photographic images of terrain. Typically, a camera is fixedly maintained on board the aircraft, receiving and storing images of the terrain below as the aircraft passes thereover. Such stored images are then used for purposes of locating and identifying various features in the terrain for subsquent purposes.
In FIG. 1 there is shown an electro-optical image system designated generally by the numeral 10 of the type which would typically be carried on an aircraft. In such a system, a lens 12 is maintained in fixed relationship to an image receiving device such as a linear array of charge coupled devices 14. Obviously, the linear array 14 is maintained at the focal length of the lens 12 to appropriately receive the desired images. It has previously been known in the art that the linear array 14 would consist of a single line of charge coupled devices, for example 10,000 or more, each receiving a discrete portion of the total image viewed, and converting that image into a charge or voltage characteristic of the light received by the charge coupled device from the object being viewed. Such a charge can then be correlated to a gray scale for generating an electronic image, or may be digitized for generation of a digital image. In any event, it should be understood that the linear array 14 views a field of view 16 through the lens 12 and generates a linear array of picture elements or pixels corresponding to the view. With a linear array, the field of view 16 is correspondingly linear such that as the aircraft travels and progressive images are continuously generated, a total view of the terrain is generated as a rectangular field of view.
Of particular concern in the prior art is distortion in the image received by the linear array 14 as a result of aircraft movement while the image is being generated. If the aircraft departs from a fixed forward velocity while the linear array 14 is being scanned, the digital image will be distorted as a function of such movement. Typically, pitch, roll, or yaw of the aircraft will tend to distort the final image. Accordingly, there is a need for correcting or compensating for the distortion resulting from such movement. Indeed, the fidelity of the final image is a function of the uncompensated aircraft motion.
Previously, it has been known to use inertial platforms on which the camera 12,14 may be mounted. Such inertial platforms measure the movement of the aircraft and provide compensation for the same. However, these electro-mechanical devices are extremely expensive to purchase and maintain and are delicate in operation.
There is in the art a need for a totally electronic device for achieving compensation for aircraft movement when images are generated with a linear array as stated above. Further, such a device is desired to be both simplistic and reliable in operation while being inexpensive to implement. Prior to the concept of the instant invention, the art has been devoid of such a structure or technique.